112 Dr. Anderson's Description and Analysis of Gnrolite, 



most abundant. The rock in which these minerals are princi- 

 pallv found may be described as a basaltic amygdaloid, very soft, 

 and so vesicular that it is impossible to break even a small piece 

 without finding it filled with drusy cavities, lined with rock 

 crystal, stilbite and apophyllite. In this rock, gnrolite is never 

 found ; but there occurs also another basalt, which I imagine to 

 have been produced by a distinct eruption of basaltic matter, 

 extremely compact and uniform in its texture, the drusy cavities 

 smaller and much less frequent, rarely containing apophyllite, 

 and almost never stilbite, but having these minerals replaced by 

 gui'olite. In this basalt traces of gnrolite are by no means un- 

 common, but fine or large specimens are decidedly rai'e ; and 

 the collector must spend a considerable time in finding them ; 

 and when met with they can rarely be obtained uninjured, as 

 the mineral is apt to fly to pieces in the attempt to dislodge it. 

 During my visit to Skye, the weather was so extremely unfa- 

 vourable that I had little opportunity of pursuing the search for 

 it, but I have no doubt that it will be found pretty generally 

 spread through the more compact basalts of the neighbourhood. 

 I found traces of it at some distance from the point at which I 

 collected my specimens ; and an old wall which is passed in as- 

 cending the Storr is built of a basalt containing small weathered 

 specimens of the mineral. 



Gurolite occurs in small spherical concretions composed of thin 

 plates radiating from a centre. The external surface of each 

 concretion has an exceedingly beautiful striated appearance, 

 owing to the plates of which it is formed rising to irregidar di- 

 stances above the surface. Colour white, kistre vitreous, passing 

 into pearly when it has been exposed to the weather. In thin 

 plates it is perfectly transparent. It cleaves readily parallel to 

 the plates of which the concretions are composed. It is very 

 tough, and cannot be reduced to powder without some labour. 

 Hardness between 3 and 4. 



Before the blowpipe in the matrass it gives off water, swells 

 up and separates into thin plates, which have a fine pearly or 

 rather silvery lusti'e. On charcoal it swells up, splits into very 

 thin laminfe, and finally fuses with difficulty into an opake 

 enamel. With borax it gives a transparent and colourless glass, 

 and with soda it fuses with difficidty into an opake mass. With 

 nitrate of cobalt it gives a feeble reaction of alumina. It is 

 readily attacked by hydrochloric acid. Its analysis was very 

 simple ; the only difficulty experienced being in the selection of 

 portions which had not lost water by efflorescence, and the earlier 

 experiments on this account gave a variable amount of water. 

 The proportion of water was determined by igniting one quan- 

 tity in a platinum crucible, and another portion was treated wnth 



